page_title: Sexual selection
section_title: Toolkit of natural selection
hierarchical_section_title: Sexual selection / Theory / Toolkit of natural selection
caption_attribution_description: English: Illustration of Protarchaeopteryx, a feathered dinosaur (or a flightless bird (according to Alan Feduccia)), found in China. This is a new version of an older illustration, "Protarchaeopteryx JST 398", which was inaccurate in the reconstruction of the head and the wings. Here, the skull is based on Incisivosaurus, since the skull of Protarchaeopteryx is poorly preserved ( see 'dinoweb.narod.ru). The wings are based on Caudipteryx.
context_page_description: Sexual selection is a mode of natural selection in which members of one biological sex choose mates of the other sex to mate with, and compete with members of the same sex for access to members of the opposite sex. These two forms of selection mean that some individuals have greater reproductive success than others within a population, for example because they are more attractive or prefer more attractive partners to produce offspring. For instance, in the breeding season, sexual selection in frogs occurs with the males first gathering at the water's edge and making their mating calls: croaking. The females then arrive and choose the males with the deepest croaks and best territories. In general, males benefit from frequent mating and monopolizing access to a group of fertile females. Females can have a limited number of offspring and maximize the return on the energy they invest in reproduction.
context_section_description: Sexual selection may explain how certain characteristics (such as feathers) had distinct survival value at an early stage in their evolution. Geoffrey Miller proposes that sexual selection might have contributed by creating evolutionary modules such as Archaeopteryx feathers as sexual ornaments, at first. The earliest proto-birds such as China's Protarchaeopteryx, discovered in the early 1990s, had well-developed feathers but no sign of the top/bottom asymmetry that gives wings lift. Some have suggested that the feathers served as insulation, helping females incubate their eggs. But perhaps the feathers served as the kinds of sexual ornaments still common in most bird species, and especially in birds such as peacocks and birds-of-paradise today. If proto-bird courtship displays combined displays of forelimb feathers with energetic jumps, then the transition from display to aerodynamic functions could have been relatively smooth.
  Sexual selection sometimes generates features that may help cause a species' extinction, as has been suggested for the giant antlers of the Irish elk (Megaloceros giganteus) that became extinct in Pleistocene Europe. However, sexual selection can also do the opposite, driving species divergence—sometimes through elaborate changes in genitalia—such that new species emerge.
caption: Reconstruction of Protarchaeopteryx, an early proto-bird
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